α-substituted acroleins find application in specialty polymers and pharmaceuticals. The sequential hydroformylation—Mannich reaction for the formation of α-β unsaturated aldehydes is very well documented in literature. The reaction proposed invariably deal with the formation of an unsaturated aldehyde by condensation of two aldehyde molecules, both of which are in turn prepared by the hydrofomylation of olefins. In effect the reaction is a hydrofomylation-homoaldol reaction since the aldol reaction is mainly between two similar aldehyde molecules. The hydroformylation of propene followed by the aldol condensation of the formed butyraldehyde as a route to 2 ethyl hexanol is Very well documented and is a commercial application. In this context reference may be made to British Patent 1002429 wherein the preparation of 2 ethyl hexanol via the hydrofomylation of propene is proposed. The catalysts used in this invention relate to cobalt compounds and the reaction is carried out between the butraldehyde formed via the hydroformylation reaction. The reaction is conducted in a basic medium that is a homogeneous phases. The drawbacks are that the aldol condensation is a homoaldol formation and not a hetero-aldol reaction as proposed in the present invention.
Reference is made to U.S. Pat. No. 6,573,414 wherein the formation of C9 and C10 alcohols is achieved by a hydroformylation of butene to C5 aldehydes followed by aldol condensation to yield C10 alcohols. The drawbacks are that the different reactions involved viz hydroformylation, aldolisation and subsequent hydrogenation are carried out in multiple stage and not in a single reactor as is claimed in the present invention.
Reference is made to U.S. Pat. No. 5,689,010 wherein a single stage process for the hydroformylation and aldol condensation has been proposed. In this patent the aldol condensation is primarily between the aldehydes formed in the course of hydroformylation reaction. Due to such a system it is not possible to achieve a hetero aldol condensation which is necessary to achieve the formation of a substituted acroleins.
A one stage process for the preparation of higher aldehydes by hydroformylation-aldol condensation is described in PCT Application WO 80/01691. Herein rhodium complex catalysts have been proposed for hydroformylation of higher α-olefins. The aldol condensation is catalyzed by the presence of bases like KOH and Lewis bases. Here too only homo aldol formation is carried out.
Reference is made to U.S. Pat. No. 3,278,612 wherein the use of alkaline medium has been postulated to achieve hydroformylation-aldol condensation in the presence of cobalt catalysts. The drawbacks are that this invention pertains to homo aldol condensation.
Reference is also be made to U.S. Pat. Nos. 4,426,542, 5,463,147, 5,462,986, 5,369,162, 5,382,716 and 5,268,514 wherein a multistage process incorporating hydroformylation, followed by aldol condensation of the formed aldehydes with subsequent hydrogenation of the unsaturated aldehydes to higher alcohols is proposed. In all these patents no reference is made to the aldol condensation of two dissimilar aldehydes.
Synthesis of α-substituted acroleins by reaction of aldehydes with formaldehyde in the presence of a base is well documented in literature. [See for reference Ulllmann's Encyclopeida of Industrial Chemistry, Vol A1, page 149 to 160, 5th edition] The aldol condensation of propionaldehydes with formaldehyde to yield methacrolein is also a very well practiced process as indicated in the above reference.
Reference is made to U.S. Pat. Nos. 4,408,079 and 4,496,770 wherein aldol condensation of aldehyde and formaldehyde is reported in the presence of secondary amine catalysts to yield α-alkyl acroleins. The use of amines in the presence of organic acids is also said to improve the yield of the desired product. In these patents the aldol condensation is a unique reaction and not coupled with any other previous reaction, which generates the aldehyde. The use of a two-phase system has also not been mentioned.
In all the above mentioned prior art the following drawbacks can be summarized:    (i) Sequential hydroformylation of olefin followed by aldol condensation of the formed aldehyde with formaldehyde already present in the reaction medium, has not been mentioned.    (ii) The deactivation of the aldolisation catalysts in the presence of the hydroformylation catalysts, formaldehyde under reaction conditions has not been indicated.    (iii) The use of a strategy to segregate the two catalysts to achieve the desired synthesis of substituted acroleins has not been mentioned.